The invention pertains to a gas mixer. The invention also pertains to a gas mixing system and to a gas engine.
A gas mixer of the type indicated above is used to mix a first gas and a second gas together. Especially in the case of a gas engine, the first gas is in the form of combustion air, i.e., fresh air or a lean air/gas mixture, and the second gas is in the form of a fuel gas. The gas mixer provides an air/fuel gas mixture, consisting of combustion air and the fuel gas mixed with it, suitable for the gas engine. Especially in the case of a lean gas engine, it has been found important to adjust the lambda ratio (i.e., the ratio of fuel gas to combustion air) on the basis of, for example, the power demand of the lean gas engine. A gas mixer can be found in EP 0 898 064 A1 in the form of a venturi mixer, for example, which is installed upstream of a lean gas engine in a gas mixing system for adding fuel gas to, and mixing it with, combustion air or a lean gas mixture.
In the case of a venturi mixer, it is possible in principle to work with different cross sections to increase the mixing quality of the air/fuel gas mixture; in EP 2 258 983 A2, for example, a venturi mixer with a mixing section with different cross sections is described. GB 154,920 describes a gas mixer of the above-mentioned type with a movable displacement body in a venturi tube, as a result of which the size of a mixing gap can be adjusted to different values.
From the brochure dating from April 1988 concerning the RMG980 gas mixer from the company RMG, a gas mixer is known which comprises a fixed displacement body in a venturi tube, representing a comparatively robust design similar to the prior art shown in FIG. 1. The intake cross section for a second gas, combustion gas in particular, is formed here by first and second gas housing parts, which form the boundaries of the intake cross section. As described in the prospectus, the fixed intake cross section between the fixed gas housing parts determines the mixing ratio between the first gas (air or lean gas mixture in the venturi tube) and a second gas (fuel gas in the intake tube).
It is desirable for the intake cross section to be adjustable to different values. An adjustable part which forms the boundary of the intake cross section and which can be actuated as desired, however, can be extremely complex.
The drive for a control element for the adjustable parts forming the boundary of the intake cross section can also be complicated. Angular gears and other types of mechanical force-transmitting drives advanced by gear wheels are more susceptible to wear than other types, which means that the accuracy or speed with which adjustments can be made always deteriorates over the life of the drive.
EP 2 016 994 A describes a gas mixer of the above-mentioned type, in which a venturi tube comprises inlets for fuel gas in the area of a narrowed cross section; control elements are able to change these inlets during the mixing process. The control elements comprise here a control sleeve surrounding the narrowed cross section, the sleeve being provided with fuel control openings. Shifting the positions of the fuel control openings with respect to the inlet openings for the fuel gas changes the size of the cross sections through which the fuel gas can pass. The narrowed cross section is formed by a displacement body arranged in the venturi tube. Admittedly, it is possible by this means to achieve a comparatively precise adjustment of the open cross section; however, the corresponding automatic control process takes a comparatively long time, and/or the maximum allowable actuating force is limited. The mechanical design of the previously mentioned control elements is also comparatively complicated, which means that the accuracy of the adjustments can suffer over the life of the gas mixer as a result of a wear, and a loss of performance can also be caused by the accumulation of dirt.
It would be desirable to have a drive and a control element which can be realized in a gas mixer with comparatively few restrictions and which at the same time allow the control element which determines the intake cross sections to be positioned robustly, rapidly, and comparatively accurately over a long service life.